The phase coherent low frequency loud speaker of this invention is classified in Class 179, subclasses 181R, 181F, 115.5R and 115.5ME.
Bertagni, in U.S. Pat. No. 3,722,617 issued Mar. 27, 1973, discloses a flat diaphragm for sound transducers having a flat front face and rear face, defining a central figure portion connected to an electromagnetic assembly and surrounded by a marginal vibration damping portion of larger thickness than the adjacent peripheral zone of the figure portion.
Bertagni, in U.S. Pat. No. 3,767,005 issued Oct. 23, 1973, discloses a flat loud speaker diaphragm with means for enhancing the low frequencies wherein the diaphragm has a marginal vibration damping portion surrounding a sound producing figure portion and at least a portion of said marginal vibration damping portion is connected to a plate-like member adapted to vibrate only in the low frequency range.
Allison, in U.S. Pat. No. 4,029,910 issued June 14, 1977, discloses an audio loud speaker comprising a diaphragm which is rotationally symmetrical about a central axis, the diaphragm including a sound propagating surface extending between a larger circular edge and a small circular edge spaced apart therefrom along the axis in the direction of sound propagation. The voice coil frame is secured to the diaphragm adjacent the smaller edge, the larger circular diaphragm edge is fixed relative to the magnetic structure (e.g. to the mounting panel).
In U.S. Pat. No. 4,317,965 issued Mar. 2, 1982, Toyoda discloses a dynamic loud speaker formed with a vibration plate disposed between a yoke and a permanent magnet. The vibration plate is substantially planar with a central projecting cylindrical region. A voice coil is disposed on the vertical wall of the central projecting region of the vibration plate.
In U.S. Pat. No. 3,955,055 issued May 4, 1976, Kawakomi et al, disclose a dynamic loud speaker including a dome type diaphragm having at least one convex surface and another concave surface, contiguous with the convex surface. Specifically, the concave surface is annular portion surrounding the convex surface.